Safe load indicating devices for cranes



March 3, 1964 R. L. AITKEN SAFE LoAn INDICATING DEVICES FOR cRANEs 2 Sheets-Sheet l Filed Feb. 4, 1963 BVM/WM @KZ 25W ATTO/w55 )j /N VENTO? KMA/uh m March 3, 1964 R. L. AITKl-:N

SAFE: LOAD INDICATING DEVICES FOR cRANEs 2 Sheets-Sheet 2 Filed Feb. 4, 1963 /NvE/vro BJJMM /f/hw' ATTORNEYS f Patented Mar. 3, 1964 3,123,814 SAFE LOAD INDICATING DEVICES FOR CRANES Robert Loudon Aitken, 50 Pall Mall, London SW. 1, England Filed Feb. 4, 1963, Ser. No. 256,029 Claims priority, application Great Britain Feb. 9, 1962 Claims. (Cl. 340-267) The present invention relates to safe-load indicating devices for the type of apparatus, such as cranes and the like, which is adapted to lift a load suspended from a jib from a point, the effective radius of which in relation to the jib foot, may -be varied.

As is well-known the safe load which any particular crane can lift depends upon the jib radius at which the crane is operating.

It is well-known to provide a safe load indicator attached to the crane jib or other convenient part of the crane. Known safe-load indicators are constructed to adjust themselves automatically with changes of jib angle so asy to indicate the safe load appropriate to the operating radius.

v It should be understood that the term safe-load is used herein to define a load which is slightly less than that at which the crane would be damaged under operating conditions. Usually it is slightly less than that at which the crane would overturn, but in some cranes using long, light jibs the jib may buckle at small operating radius at a load less than that required to overturn the crane and this factor must betaken into account in determining the safe load of the crane.

It is,-in fact,`desirable to arrange that the safe-load indicator will operate two audible orvisual warning devices in succession, the first as the safe load is approached and the second as the safe load is reached. It is obviously desirable that the load at which the first indication takes place should bear a substantially constant relation to the safe load, e.g. should always be approximately 90% of the safe load or of the equivalent force on the indicator.

To achieve this result the actuation of the warning devices is preferably effected by deecting a switch operating member arranged in such manner that its deflection due to the permissible maximum safe loads on the crane at different radii is always the same in spite of the-corresponding force on the indicator being different at each different radius of the crane.

Accordingly the present invention provides a safe-load indicator comprising an operating member, adapted to' actuate at leastone warning device when an actuating portion of said member is broughtto a predetermined spacial position, saidoperating member being mounted on two pivots, said pivots being angularly movable relative to each other and likewise being movable relative to each other lengthwise of the operating member, means causing relative movement between said pivots lengthwise of `the operating member ,so that their relative distance from oneanother is a function of the inclination of a crane jib, means causing relative angular movement of said pivots so that such relative angular movement is a function of the crane load, said means being arranged to move one of said pivot points through a distance which is substantially proportional to a force4 derived from the crane load.

Conveniently a safe-load indicator comprises a lever pivoted at a fixed point, upon which lever the force derived from a crane load is imposed against resilient restoring means to deflectsaid lever, said operating member being pivotally connected to the lever by a pivot which is immovable lengthwise of said operating member, a second pivot engaging in a track in said operating member lfor movement lengthwise of said operating membeing moved relative to the frame 4 by change of jib ber and means for moving said second pivot lengthwise of operating member arranged so that the distance between said pivots is a function of the inclination of the jib of the crane.

In addition this invention provides a safe-load indicator in which the operating member is pivoted on a fixed pivot and has a second pivot movable along a track lengthwise of said operating member and comprising means for moving said second pivot along said track, arranged so that the distance of the second pivot from the first p ivot is a function of the jib inclination and means connecting said second pivot to a point on a lever, pivoted to a fixed point, upon which lever the force derived from a crane load is imposed against resilient restoring means to deflect said lever.

The resilient restoring means against which the crane force is applied may be a coil spring, in tension or compression, a volume of compressed gas, a compressible block such as a rubber block or any other resilient member against which a load can be applied.

In order that the present invention may be more clearly understood two embodiments will now be described, by way of example, with reference to the following drawings in which:

FIGURE 1 shows a side elevation of one embodiment of the invention,

FIGURE 2 shows a side elevation of another embodiment of the invention, and

FIGURE 3 is a section along the line III- III of FIG- URE 2.

' A crane loading derived in the conventional manner from the hoist rope, derricking rope or other element, is appliedin tension through a link 1 to a lever 2 mounted on pivot 3 in the indicator frame 4. Link 1 is connected to the lever 2 by a pin 5. At the end of the lever 2 remote from the pivot 3 a restoring spring 7 is attached at point 6 to the lever 2 and the other end of spring 7 is attached through an adjustment device 9 to a lug 8 mounted on the frame 4.

An operating member in the form of a lever 11 is pivotally connected with the lever 2 at a first pivot 10 on a lug extending from lever 2.

A link 12 is connected to a lever 12a, which is connected to a cam 13 so as to turn the cam 13 about the axis of a shaft 14 to an appropriate position, the link 12 inclination. A double lever 15, carrying a cam follower 16, is pivotally mounted on a pin 17 in the frame 4 and a spring 19 connected to the lever 15 holds the cam follower 16 against the cam 13. At the end of lever 1S remote from the pivot pin 17 is a cross-head 18, constituting the second pivot of the operating member and slidably mounted in a straight slot 20 in lever 11. The slot 20 can alternatively be curved but should not conform to the path of cross-head 18. At the other end of lever 11 there are mounted switch actuating members 24 and 25 arranged respectively to actuate conventional spring-loaded limit switches 26 and 27 mounted on frame 4.

In operation the crane loading is applied to link 1 and tends to draw up lever Ziagainst the restoring force from spring 7 and the force exerted by the spring can be adjusted'using adjuster 9. This movement also draws up lever 11 through pivot 10 by which lever 11 is connected to lever 2. The cross-head 18 moves in the slot 20 to a position appropriate to the jib angle on change of position of the link 12 relative to the frame 4 and so changes the distance between the pivot point 10 and the pivot constituted ,by the cross-head 18. Movement of the cross-head 18 alters the angular movement of lever 11 produced by a given crane force applied through connect the cross-head with the link 51.

the link which is` the operating member and so compounds the loading and crane radius at which switch actuating members 24 and 25 actuate switches 26'and 27.

By suitably .positioning the .switches and the respectiveV the safe load in cases where itis desired to use a switch to stop the crane motors.

In the indicator shown in FIGURE 2 a crane loading is applied by link 31 and pin 35 to a lever 32 pivotally mounted on pin `33 in the indicator frame 34. A ylink 42 is connected to an arm 42a, which turns a cam 43` about the axis of a shaft or pin 44. A cam lever 45, carrying a cam follower 46 arranged to follow the Vcam face of cam 43, -is secured to a shaft 47 to which lever 48 is also secured. The'lever 48 is secured to one end of a wireV 56 which extends .to a cross-head 54 on anV operating member.V The operating member is in the form of a `bell-crank lever 49 ypivotally mounted on a pin 50 carried in the frame 34 and constituting the iirst pivot of the operating member. The second pivot of the operating lmember is constituted by pivot pins 53, which are carried by the cross-head member 54, longitudinally slidable on one Varm of the bell-crank lever 49. The cross-head is connected by the pins 53 to a link 51, which isV in turn Vconnected by a pivot pin V52 to the lever 32. The cross-head 54 is connected by the wire 56 to the lever 48 passing over a pulley 57 arranged so that the wire passes substantially through Vthe Aaxis of the pivot 50, 'so that tilting of the lever 50 does not itself cause movement of the cross-head 54. A helical spring 55 holds the wire `56 taut and causes cam followerV 46 to follow the face of cam v43.

In operation a `movement corresponding -to the-'craneY load is applied to the cross-head 54 through lpins 53 which angle causes movement of link 42 relative to the frame 34 and thus causes rotation of the cam 43 which is translated through lever 48 and wire 5.6 to movement of the cross-head 54 lengthwise Vof the arm of the lever 49 on which -it is lg'uided, thus altering the distance between the first and second pivot` points of the operating member. Actuatingmembers .58 and 59 are mounted on lever 49 and actuate switches 60and 61 in the same Y manner as Ydescribed with reference to FIGURE 1.1

. I claim:

1. A safe-load' indicator comprising an operating member, adapted Vto actuate at least one warning device when an actuating portionrofV said Y member is brought to a movable relative to each other and likewisebeing lmov- VYable'relative to each other lengthwise of the operating Change of jib Y member, means causingrrelativeV movement between said pivots :lengthwise of theoperating member `so that their relative distance'fromgone another is a function of the Vinclination of a crane'jibfmcans causing relative angular Amovement of Vsaid pivots so that such .relative angular movement is a function ofthe crane load, said means being arranged to move one Vof said pivot points through i a distance which is substantially proportional toa force derived from the crane load. Y Y f 42.V A safe-load indicator V'accordingto' claim 1 Vcomprising a lever pivoted atafiixed point, upon which lever "the force derived from a crane load'is imposed against resilient restoringmeans :todeflect said lever, said opposed. f 50 Y vthe linkage is inthe form of an inextensible ilexible eratingV member being pivotally connected to the lever by a pivot which is immovable lengthwise of said operating member, a second pivot engaging in a trackin said operating member for movement lengthwise'of said operating member and means for moving said second pivot lengthwise of operating member arranged so that the distance between said pivots is a function of the inclination of the jib of the crane.

3. A safe-load indicator according to claim 2 in which the track in said operating member is in the form of a slot and in which the second pivot is in the form of a cross-head lslidably engaging in said slot.

4. A safe-load indicator according to claim 3 in which the cross-head is mounted at one end of a lever pivoted at its other end which lever carriesA a cam follower, bearing on a cam which is turned in response to change in the inclination of the jibVV of the `crane to move the cross-head lengthwise of the operating'mernber relative to the other pivot( 5. Asafe-load indicator according to claim 1 in which the operating member is pivoted on a fixed pivot Vand has a second pivot movable .along a track lengthwise of said operating member and comprising means for moving said second pivot along said track, arranged so lthat the distance of thesecond pivot from the rstpivot is a funcwhich said second pivot can lbe moved.V

7. Aisafe-'load indicator according'to claim 6 in which means for moving saidV second pivot lengthwise of said track comprises a pivotally mounted lever carrying a cam follower arranged to bear on a cam vmovable in response to change of the inclination of the crane jib and alink-V age connecting Vthe end of said lever remote from its pivot with the second pivot, said linkage being arranged to maintain said second pivot Vat a'p'redetermined position lengthwise of said track irrespective of ,the angular position of Asaid bell-crank lever about the rst pivot.

8.V A safe-load indicator according to claim 6 in which the lsecond pivot is in the form of a cross-head movable on saidV other arm said cross-head being `carried by a link connected withfthe yleverpn which a craneload is im# 9. A safe-load indicator according to claim 8 in which member passing downran axial guideway in said other armioftheoperating .member tothe cross-head, resilient means holding said flexible member taut.

10./A safe-load indicator as claimed in claim V1 in `which the operating member carries two switch actuatingr members VVarranged yto actuate warning devices 'ref' spectively at a load a predetermined amount less than the maximum: safe load and at said maximumsafe load.

References Cited in the le of this patent UNITED STATES PATENTS Y 1,778,037l okay 1-70ct 14, i930 Y, Y FOREIGN PATENTS 394,660(` Great Britain June 211933 

1. A SAFE-LOAD INDICATOR COMPRISING AN OPERATING MEMBER, ADAPTED TO ACTUATE AT LEAST ONE WARNING DEVICE WHEN AN ACTUATING PORTION OF SAID MEMBER IS BROUGHT TO A PREDETERMINED SPACIAL POSITION, SAID OPERATING MEMBER BEING MOUNTED ON TWO PIVOTS, SAID PIVOTS BEING ANGULARLY MOVABLE RELATIVE TO EACH OTHER AND LIKEWISE BEING MOVABLE RELATIVE TO EACH OTHER LENGTHWISE OF THE OPERATING MEMBER, MEANS CAUSING RELATIVE MOVEMENT BETWEEN SAID PIVOTS LENGTHWISE OF THE OPERATING MEMBER SO THAT THEIR RELATIVE DISTANCE FROM ONE ANOTHER IS A FUNCTION OF THE INCLINATION OF A CRANE JIB, MEANS CAUSING RELATIVE ANGULAR MOVEMENT OF SAID PIVOTS SO THAT SUCH RELATIVE ANGULAR MOVEMENT IS A FUNCTION OF THE CRANE LOAD, SAID MEANS BEING ARRANGED TO MOVE ONE OF SAID PIVOT POINTS THROUGH A DISTANCE WHICH IS SUBSTANTIALLY PROPORTIONAL TO A FORCE DERIVED FROM THE CRANE LOAD. 